[PECOFF] Use Windows style options instead of Unix style as primary options.

LLD still accepts both Unix and Windows style options when it's run as
link.exe. This patch does not change functionality.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@187086 91177308-0d34-0410-b5e6-96231b3b80d8